This invention relates to a storage system to store data used by computers and more specifically to a storage system that allows the capacity of storage accessed by computers to be changed.
The storage capacity of a conventional storage system depends on the capacity of disk drives or other similar physical devices installed in the system. Therefore, when required to have a large storage capacity, a storage system has to be equipped with an accordingly large number of physical devices. While there is a demand for a large storage capacity, users also make a conflicting demand for reduction in cost and size.
Here comes an urgent need to develop a mechanism that enables a storage system to change its storage capacity dynamically. One of methods known to be useful in building such a storage system is automatic storage device capacity expansion (see JP 2003-15915 A, for example). In this method, a logical block address in a read or write I/O request at which a host computer accesses a logical volume of a storage device is monitored. Then, with the obtained logical block address as the key, the storage area of the logical volume is dynamically expanded. This method also allows a command unit of a host computer to send a logical volume capacity reduction/expansion instruction to a volume server, which then reduces/expands the storage area of the logical volume.
The prior art publication discloses that the capacity of a device accessed by a host computer can be changed dynamically, but not how the technique is applied. In particular, the prior art publication does not disclose how logical volumes are set in virtual volumes and how the set volumes are to be utilized in the case where virtual volumes are utilized for a storage system.
This invention has been made in view of the above problems, and it is therefore an object of this invention to provide a computer system capable of changing the storage capacity of a storage system that utilizes virtual volumes.